1. Field of Invention
The present invention relates to a liquid crystal alignment solution and more particularly to a liquid crystal alignment solution which can enhance the performance of a liquid crystal display device.
2. Description of Related Art
A liquid crystal display (LCD) is a display device utilizing the characteristics of liquid crystal molecules. The orientation of liquid crystal molecules is changed as an electric field is changed, so as to control the light transmitted through the liquid crystal layer to produce an image. The liquid crystal display becomes the mainstream in recent years due to the advantages of small volume, light weight, low power consumption and good display quality.
The main fabrication process of the liquid crystal display includes fabricating a liquid crystal panel and assembling a liquid crystal module (LCM). The method of forming the liquid crystal panel mainly includes sealing liquid crystal molecules between a color filter serving as an upper substrate and a thin film transistor (TFT) serving as a lower substrate. It is important for the liquid crystal display to have the long axial direction of liquid crystal molecules aligned with the surface of the substrate at a pre-tilt angle uniformly. The material which can orient liquid crystal molecules at a pre-tilt angle is called an alignment layer.
Two typical fabrication methods of forming the alignment layer are known in the industry. The first method is forming an inorganic film by steam depositing an inorganic material. For example, the film is formed by an oblique angle deposition of silicon oxide on a substrate, and liquid crystal molecules are oriented in the direction of deposition. The above-mentioned method can obtain a uniform orientation of liquid crystal molecules, but it does not meet the economics of industry. The second method is coating an organic film on the surface of a substrate, and then rubbing the organic film by a rubber or a cloth (cotton, nylon or polyester) to determine the orientation; thus, liquid crystal molecules are oriented in the direction of rubbing. This method is simple and easy to obtain a uniform orientation of liquid crystal molecules, so it is widely used in the industry. The polymer for forming the organic film is polyvinylalcohol (PVA), polyethylene oxide (PEO), polyamide (PA) or polyimide (PI), for example. Due to the chemical resistance and thermal stability, polyimide is the most frequently used material as an alignment layer material.
Conventionally, when a voltage is applied to the liquid crystal display device, the ionic electrons are absorbed by the alignment layer. However, when the voltage is interrupted, the ionic electrons are not separated from the alignment layer completely so that the remaining image is resulted. Therefore, the recent development of the alignment layer material mainly focuses on reducing the remaining image.